Method for manufacturing semiconductor substrate

ABSTRACT

A semiconductor substrate is provided in which an alignment mark is formed that can be used for an alignment even after the formation of an impurity diffused layer by the planarization of an epitaxial film. A trench is formed in an alignment region of an N − -type layer formed on an N + -type substrate. This trench is used to leave voids after the formation of a P − -type epitaxial film on the N − -type layer. Then, the voids formed in the N − -type layer can be used as an alignment mark. Thus, such a semiconductor substrate can be used to provide an alignment in the subsequent step of manufacturing the semiconductor apparatus. Thus, the respective components constituting the semiconductor apparatus can be formed at desired positions accurately.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of pending U.S. application Ser. No.12/964,141, filed on Dec. 9, 2010, which is a divisional of pending U.S.application Ser. No. 12/089,497, filed on Apr. 7, 2008, which is a U.S.National Phase Application of PCT/JP2006/319933, filed Oct. 5, 2006,which claims priority of Japanese Application No. 2005/293087, filedOct. 6, 2005, and Japanese Application No. 2006/214551, filed on Aug. 7,2006, the disclosure of each of which is expressly incorporated hereinby reference in its entirety.

TECHNICAL FIELD

The present invention relates to a semiconductor substrate that ispreferred for the manufacture of a semiconductor apparatus that uses atrench formed in a depth direction of the substrate with a high aspectratio such as a MOSFET and a super junction MOSFET having athree-dimensional structure and the method for manufacturing the same.

BACKGROUND ART

Conventionally, a semiconductor apparatus that uses a trench formed in adepth direction of a substrate with a high aspect ratio (e.g., MOSFET(see Patent Publication 1 for example), super junction MOSFET (seePatent Publication 2 for example) has been known. A semiconductorapparatus having the structure as described above forms an impuritydiffused layer having a high aspect ratio by burying an epitaxial filmin a trench (see Patent Publications 3 and 4 for example).

-   Patent Publication 1: Japanese Unexamined Patent Application    Publication No. 2001-274398-   Patent Publication 2: Japanese Unexamined Patent Application    Publication No. 2003-124464-   Patent Publication 3: Japanese Unexamined Patent Application    Publication No. 2001-196573-   Patent Publication 4: Japanese Unexamined Patent Application    Publication No. 2005-317905

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

When an impurity diffused layer having a high aspect ratio is formed byburying an epitaxial film in a trench, a method for manufacturing asemiconductor substrate as described below can be considered forexample. FIG. 8 is a sectional view of an example of a part of the stepsof manufacturing the same.

First, a semiconductor substrate is prepared structured as shown in FIG.8( a) so that an N⁻-type layer 102 is formed on an N⁺-type substrate101. Then, a mask (not shown) is used to form trenches 103 having aplurality of high aspect ratios in a device formation region of theN⁻-type layer 102 as shown in FIG. 8( b). At the same time, a trench 104is also formed in an alignment region exterior to the device formationregion as an alignment mark in a subsequent step. Then, an epitaxialfilm 105 is grown under conditions in which impurity is doped so as tobury the trench 103 as shown in FIG. 8( c). Thereafter, the epitaxialfilm 105 formed at the upper part of the trench 103 is subjected to aplanarization processing step in which the epitaxial film 105 isplanarized to eliminate an uneven part, thereby forming an impuritydiffused layer 106 as shown in FIG. 8( d).

As described above, when the epitaxial film 105 is buried in the trench103 to form the impurity diffused layer 106 having a high aspect ratio,a planarization processing step is used to planarize the uneven part ofthe epitaxial film 105.

However, when the epitaxial film 105 is buried in the trench 103, theepitaxial film 105 is also buried in the trench 104 formed in thealignment region and thus the uneven part of the trench 104 iseliminated after the planarization processing step. Then, the epitaxialfilm 105 grows in single crystal to a substrate or a silicon layer as abase. Thus, the existence of only a pure material diffusion layer isrecognized in the trench 104 formed in the alignment region as well. Incontrast with an oxidized film or non-polycrystalline silicon, such asingle crystal impurity diffused layer makes difficult to recognize aninterface between an N⁺-type substrate 101 and an N⁻-type layer 102formed by single crystals by an optical manner or by laser (He—Ne). As aresult, the trench 104 formed in the alignment region cannot be used asan alignment mark for the alignment in the subsequent step.

On the other hand, a conventional method for manufacturing asemiconductor substrate buries an epitaxial film in previously-formedtrenches a plurality of times to form a diffusion layer having a highaspect ratio. Thus, the aspect ratio can be increased to a limitedlevel. When the aspect ratio of the trenches is increased to a levelexceeding the limit, the epitaxial film buried in the trenches may havea burying defect (void). The generation of the void may cause flakedownat the upper part of the void to reduce the breakdown voltage, thuscausing a deteriorated element performance.

In particular, in order to improve the breakdown voltage of theabove-described super junction structure (P/N column structure) in whichan N-type region and a P-type region are alternately arranged in adirection orthogonal to the current direction, the trench depth must beincreased. However, when an increased trench depth causes an increasedaspect ratio to cause a burying defect (void) in the epitaxial filmburied in the trenches, the burying defect (void) causes a crystal faultto reduce the yield of the junction leak and breakdown voltage or toleave resist at a defective burying portion of a trench to cause anin-process contamination.

It is the first objective of the present invention to provide asemiconductor substrate having an alignment mark that can be used foralignment even after an epitaxial film is planarized to form an impuritydiffused layer and the method for manufacturing thereof.

It is the second objective of the present invention to provide a methodfor manufacturing a semiconductor substrate by which a void can beprevented from being generated in an epitaxial film buried in a trench.

Means for Solving the Problem

In order to achieve the first objective, the first characteristic of thepresent invention is that a semiconductor substrate has a substrate (1)made of single crystal semiconductor and a semiconductor layer (2) madeof single crystal formed on the surface of the substrate (1). Voids (3)as an alignment mark are formed in the substrate (1) in an alignmentregion in the substrate (1) that is different from a device formationregion.

In the semiconductor substrate having the structure as described above,the voids formed in the alignment region can be optically recognized forexample to the substrate made of single crystal semiconductor. Thus, thevoids can be used as an alignment mark to form a trench in asemiconductor layer included in the semiconductor substrate for exampleto provide alignment for the manufacture of a semiconductor apparatussuch as a MOSFET and a super junction MOSFET having a three-dimensionalstructure.

The second characteristic of the present invention is that asemiconductor has a substrate (21) made of single crystal semiconductorand a semiconductor layer (22) made of single crystal formed on thesurface of the substrate. Voids (25) as an alignment mark are formed inthe semiconductor layer in an alignment region in the semiconductorlayer that is different from a device formation region.

As described above, the same effect as that of the first characteristicalso can be obtained by the above structure in which voids as analignment mark are formed in the semiconductor layer.

In these cases, a trench (4, 23) may be formed in a device formationregion of the semiconductor layer and an epitaxially-grown impuritydiffused layer (5, 24) may be formed in the trench.

A single void or a plurality of voids may be used. A plurality of voidsarranged with an equal interval for example can be easily recognized asvoids formed an alignment mark.

The semiconductor substrate having the first characteristic ismanufactured by a method for manufacturing that includes, for example, astep of preparing a substrate (1) made of single crystal semiconductor;a step of arranging, on the substrate, a mask material (10) in which anopening is formed in the alignment region in the substrate differentfrom a device formation region; and a step of etching the substratecovered by the mask material to form an alignment mark formation trench(11) in the alignment region; and a step of forming a semiconductorlayer (2) made of single crystal on the surface of the substrate so asto form voids (3) in the alignment mark formation trench.

In this case, the step of forming an alignment mark formation trenchpreferably forms the alignment mark formation trench having a width of 1to 50 μm for example.

The semiconductor substrate having the second characteristic ismanufactured by a method for manufacturing that includes, for example, astep of preparing a substrate (21) made of single crystal semiconductor;a step of forming a semiconductor layer (22) made of single crystal onthe surface of the substrate; a step of arranging a first mask material(30) on the semiconductor layer, the first mask material (30) includesan opening formed in an alignment region in the semiconductor layerdifferent from a device formation region; a step of etching thesemiconductor layer covered by the first mask material to form analignment mark formation trench (31) in the alignment region; a step ofremoving the first mask material to place, on the surface of thesemiconductor layer, a second mask material (32) in which an opening isformed in the device formation region of the semiconductor layer; a stepof etching the semiconductor layer covered by the second mask materialto form a device trench (23) in the device formation region; a step ofremoving the second mask material to bury an epitaxial film (33) in thedevice trench so as to form voids (25) in the alignment mark formationtrench; and a step of subjecting, to a planarization processing, a partof the epitaxial film that is formed exterior to the device trench.

As described here, instead of performing the step of forming thealignment mark formation trench in the alignment region prior to thestep of forming the device trench in the device formation region, thestep of forming the alignment mark formation trench in the alignmentregion also may be performed after the step of forming the device trenchin the device formation region.

In these cases, the step of forming an alignment mark formation trenchpreferably forms the alignment mark formation trench to have a depthdeeper than the width of the device trench. This can easily form theepitaxial film to bury the device trench while forming the voids in thealignment mark formation trench.

For example, the alignment mark formation trench can have a depth atwhich the substrate can be etched.

Furthermore, the formation of the alignment mark formation trench in thealignment region also may be simultaneously performed with the formationof the device trench in the device formation region. This can simplifythe steps of manufacturing the semiconductor substrate.

In the method for manufacturing a semiconductor substrate having thesecond characteristic as described above, the alignment mark formationtrench preferably has a width smaller than that of the device trench.This can easily form the epitaxial film to bury the device trench whileforming voids in the alignment mark formation trench.

It is noted that reference numerals in the parentheses show thecorrespondences with specific means described in the embodimentsdescribed later.

The invention according to claim 13 is for achieving the above secondobjective. As shown in FIG. 7, the invention is a method formanufacturing a semiconductor substrate that includes: (a) a step ofgrowing a first epitaxial film 61 on the surface of a substrate body 63;(b) a step of partially etching the first epitaxial film 61 to form aplurality of first trenches 64; (c) a step of growing a second epitaxialfilm 62 on the entire interior of the plurality of the first trenches 64and the surface of the first epitaxial film 61 except for the pluralityof the first trenches 64; (d) a step of polishing the second epitaxialfilm 62 to expose the surface of the first epitaxial film 61 andplanarizing the upper face of the second epitaxial film 62 buried in theentire interior of the plurality of the first trenches 64; (e) a step offurther growing a third epitaxial film 66 having the same composition asthat of the first epitaxial film 61 on the upper face of the planarizedsecond epitaxial film 62 and the exposed face of the first epitaxialfilm 61; (f) a step of etching a part of the third epitaxial film 66corresponding to the plurality of the first trenches 64 to form aplurality of second trenches 67 to extend the plurality of firsttrenches 64; (g) a step of further growing a fourth epitaxial film 68 onthe entire interior of the plurality of second trenches 67 and thesurface of the third epitaxial film 66 except for the plurality ofsecond trenches 67; and (h) a step of polishing the fourth epitaxialfilm 68 to expose the surface of the third epitaxial film 66 andplanarizing the upper face of the fourth epitaxial film 68 buried in theentire interior of the plurality of the second trenches 67.

With regards to whether the epitaxial films 62 and 68 can be buried inthe trenches 64 and 67 without causing a void, the shallower the depth Bof the trenches 64 and 67 is to the width A of the trenches 64 and 67,the epitaxial films 62 and 68 can be buried in the trenches 64 and 67without causing a void.

In the method for manufacturing a semiconductor substrate according toclaim 13, the formation of the trenches 64 and 67 and the burying of theepitaxial films 62 and 68 are performed by a plurality of steps. Thus,when the epitaxial films 62 and 68 are buried in the trenches 64 and 67,the depth B of the trenches 64 and 67 to the width A of the trenches 64and 67 can be reduced. Thus, the epitaxial films 62 and 68 can be buriedin the trenches 64 and 67 without causing a void in the trenches 64 and67.

The invention according to claim 14 is the invention according to claim13 and is characterized in that the step (g) is followed by therepetition of the step (d) to the step (g) one or two times or more.

In the method for manufacturing a semiconductor substrate according toclaim 14, the step (d) to the step (g) are repeated three times or more.Thus, even when an aspect ratio of the trenches to be finally obtainedis relatively high, the depth B of the trenches to the width A of thetrenches when the epitaxial film is buried one time can be reduced. Thiscan effectively prevent a void from being generated in the epitaxialfilm buried in the trenches.

Effect of the Invention

As described above, according to the present invention, in an alignmentregion in a substrate different from a device formation region, a voidas an alignment mark was formed. This void can be optically recognizedto a substrate formed by single crystal semiconductor for example. Thus,this void can be used as an alignment mark to form a trench in asemiconductor layer provided in a semiconductor substrate for example toprovide the alignment for manufacturing a semiconductor apparatus suchas a MOSFET and a super junction MOSFET having a three-dimensionalstructure. In this case, in an alignment region in a semiconductor layerdifferent from a device formation region, a semiconductor layer also mayinclude a void as an alignment mark.

When the formation of a trench and the burying of an epitaxial film areseparately performed a plurality of times, the trench can have a shallowdepth to the width of the trench when the epitaxial film is buried andthus the epitaxial film can be buried in a plurality of trenches withoutcausing a void in the trenches. In particular, if the formation of atrench and the burying of an epitaxial film are repeated three times ormore, the trench can have a sufficiently-shallow depth to the depth ofthe trench in which the epitaxial film is buried even when a trench tobe obtained finally has a relatively high aspect ratio. This caneffectively avoid a void caused in an epitaxial film buried in thetrench.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the sectional structure of a semiconductor substrateof the first embodiment of the present invention;

FIG. 2 is a sectional view of steps of manufacturing a semiconductorapparatus using a semiconductor substrate manufactured by steps ofmanufacturing including the steps of manufacturing the semiconductorsubstrate shown in FIG. 1;

FIG. 3 is a view of the sectional structure of a semiconductor substrateof the second embodiment of the present invention;

FIG. 4 is a sectional view of steps of manufacturing a semiconductorapparatus using a semiconductor substrate manufactured by steps ofmanufacturing including the steps of manufacturing the semiconductorsubstrate shown in FIG. 3;

FIG. 5 is a sectional view of steps of manufacturing a semiconductorapparatus using a semiconductor substrate manufactured by manufacturesteps including the manufacture steps of a semiconductor substrateaccording to the third embodiment of the present invention;

FIG. 6 is a sectional view of manufacture steps of a semiconductorapparatus using a semiconductor substrate manufactured by manufacturesteps including the manufacture steps of a semiconductor substrateaccording to the fourth embodiment of the present invention;

FIG. 7 is a view of steps of a method for manufacturing a semiconductorsubstrate of the fifth embodiment of the present invention; and

FIG. 8 is a sectional view of manufacture steps of a semiconductorapparatus based on the examination by the present inventors.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 N⁺-type substrate    -   2 N⁻-type layer    -   3 Void    -   4 Trench    -   5 Impurity diffused layer    -   6 N⁻-type layer    -   10 Mask material    -   11 Trench    -   12 Oxidized film    -   13 Epitaxial film    -   21 N⁺-type substrate    -   22 N⁻-type layer    -   23 Trench    -   24 Impurity diffused layer    -   25 Void    -   26 N⁻-type layer    -   30 Mask material    -   31 Trench    -   32 Oxidized film    -   33 Epitaxial film    -   60 Semiconductor substrate    -   61 First epitaxial film    -   62 Second epitaxial film    -   63 Substrate body    -   64 First trench    -   66 Third epitaxial film    -   67 Second trench    -   68 Fourth epitaxial film

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. In the respective embodiments shown below,the same or similar components will be denoted with the same referencenumerals.

First Embodiment

The first embodiment of the present invention will be described. FIG. 1is a sectional view of a semiconductor substrate of the firstembodiment. As shown in FIG. 1, an N⁺-type substrate 1 made of singlecrystal silicon has thereon an N⁻-type layer 2 made of single crystalsilicon to constitute a semiconductor substrate. This semiconductorsubstrate is structured so that an alignment region of the N⁺-typesubstrate 1 (specifically, a position different from a device formationregion) has voids 3 in the N⁺-type substrate 1. These voids 3 are formedwith an equal interval thereamong for example.

In the semiconductor substrate having the structure as described above,the voids 3 formed in the alignment region can be optically recognizedfor example to the N⁺-type substrate 1 made of single crystal silicon.Thus, these voids 3 can be used as an alignment mark to form a trench inthe N⁻-type layer 2 provided in the semiconductor substrate for exampleto provide alignment in the manufacture of a semiconductor apparatussuch as a MOSFET and a super junction MOSFET having a three-dimensionalstructure.

Next, the following section will be describe a method for manufacturinga semiconductor apparatus using a semiconductor substrate including amethod for manufacturing the semiconductor substrate having thestructure as described above. FIG. 2 is a sectional view of manufacturesteps of a semiconductor apparatus using a semiconductor substratemanufactured by manufacture steps including the manufacture steps of thesemiconductor substrate shown in FIG. 1.

First, in a step shown in FIG. 2( a), the N⁺-type substrate 1 made ofsingle crystal silicon is prepared and the N⁺-type substrate 1 hasthereon a mask material 10 such as resist. Then, in the alignmentregion, positions in the mask material 10 at which the voids 3 as analignment mark are to be formed are opened. As a result, openings havingan identical width are formed in the mask material 10 with an equalinterval for example.

Next, in a step shown in FIG. 2( b), the N⁺-type substrate 1 covered bythe mask material 10 is etched to form, in the alignment region of theN⁺-type substrate 1, the trenches 11 having an identical width arrangedwith an equal interval for example. The trench 11 has a width of 50 μmor less, a depth of 1 μm or more, and has a thickness equal to or lowerthan that of the N⁺-type substrate 1. The trench 11 may be etched, forexample, by an anisotropic dry etching using Reactive Ion Etching (RIE)or an anisotropic wet etching using TMAH or KOH for example.

In a step shown in FIG. 2( c), the N⁻-type layer 2 is epitaxially grownon the surface of the N⁺-type substrate 1. In this step, the epitaxialgrowth at the surface of the N⁺-type substrate 1 can be promoted whilesuppressing the epitaxial growth into the trenches 11 formed in theN⁺-type substrate 1.

For example, any of monosilane (SiH), disilane (SiH), dichlorosilane(SiH₂Cl₂), trichlorosilane (SiHCl₃), and silicon tetrachloride (SiCl₄)is used as semiconductor source gas for epitaxial growth. In particular,any of dichlorosilane (SiH₂Cl₂), trichlorosilane (SiHCl₃), and silicontetrachloride (SiCl₄) may be used as silicon source gas.

At this time, preferable conditions are that no epitaxial film is grownin the trench 11. However, an epitaxial film may be grown so as not toentirely bury the trench 11. Thus, a region of the trench 11 on which noepitaxial film is formed is left as the void 3 in the surface of theN⁺-type substrate 1.

In a step shown in FIG. 2( d), an oxidized film 12 by thermal oxidationor CVD or the like is formed on the N⁻-type layer 2 as mask material.Then, a desired position of the oxidized film 12 can be accuratelyetched in a device formation region to open the position by using thevoid 3 as an alignment mark to provide alignment with an etching mask ofthe oxidized film 12. Then, the N-type layer 2 is etched by using theoxidized film 12 as mask material to form a plurality of trenches 4 inthe N⁻-type layer 2 arranged with an equal interval.

In a step shown in FIG. 2( e), the oxidized film 12 used as maskmaterial is removed to subsequently form a P-type epitaxial film 13 forexample so as to bury the trenches 4. This formation is performed basedon conditions according to which a rate control can be provided topromote the growth of the epitaxial film 13 into the trenches 4 formedin the N⁻-type layer 2.

For example, semiconductor source gas (silicon source gas) for epitaxialgrowth composed of any of monosilane (SiH₄), disilane (Si₂H₆),dichlorosilane (SiH₂Cl₂), trichiorosilane (SiHCl₃), and silicontetrachloride (SiCl₄) can be used to further suppress a defect or a voidin the buried epitaxial film. In particular, any of dichiorosilane(SiH₂Cl₂), trichiorosilane (SiHCl₃), and silicon tetrachloride (SiCl₄)may be used as silicon source gas. Halide gas composed of any ofhydrogen chloride (HCl), chlorine (Cl₂), fluorine (F₂), chlorinetrifluoride (CIF₃), hydrogen fluoride (HF), and hydrogen bromide (HBr)can be used to mix the halide gas with silicon source gas to form anepitaxial film. Thus, the resultant buried epitaxial film can besuppressed from including a void or a defect.

An upper limit value of the film formation temperature is 950 degreeswhen monosilane or disilane is used as semiconductor source gas, 1100degrees when dichiorosilane is used as semiconductor source gas, 1150degrees when trichiorosilane is used as semiconductor source gas, or1200 degrees when silicon tetrachloride is used as semiconductor sourcegas. A lower limit value of the growth temperature is 800 degrees whenthe film formation vacuum degree is in a range from a normal pressure to100 Pa and is 600 degrees when the film formation vacuum degree is in arange of 100 Pa to 1×10⁻⁵ Pa. An experiment shows that this lower limitvalue can provide epitaxial growth without causing crystal fault.

Thereafter, in a step shown in FIG. 2( f), the uneven part of theepitaxial film 13 is eliminated by a planarization processing step byChemical Mechanical Polishing (CMP) for example. As a result, theepitaxial film 13 is left in the trench 4 to form an impurity diffusedlayer 5.

Thereafter, as shown in a step of FIG. 2( g) for example, a step ofmanufacturing a remaining semiconductor apparatus is performed as asubsequent step by forming an N⁻-type layer 6 on the N⁻-type layer 2 andthe impurity diffused layer 5 for example, thereby completing thesemiconductor apparatus using the trench 4 having a high aspect ratio.This step also can use the void 3 as an alignment mark to providealignment in a photolithography step in a subsequent step to accuratelyform the respective components constituting the semiconductor apparatusat desired positions.

As described above, in the semiconductor substrate of the firstembodiment, the void 3 formed in the N⁺-type substrate 1 can be used asan alignment mark. Thus, the semiconductor substrate as described abovecan be used to provide alignment in the subsequent step of manufacturingthe semiconductor apparatus e.g., a formation step of the trench 4formed in FIG. 2( f). Therefore, the respective components constitutingthe semiconductor apparatus can be accurately formed at desiredpositions.

Second Embodiment

The second embodiment of the present invention will be described. FIG. 3is a sectional view of a semiconductor substrate of the secondembodiment. As shown in FIG. 3, an N⁺-type substrate 21 made of singlecrystal silicon has thereon an N⁻-type layer 22 made of single crystalsilicon. An impurity diffused layer 24 is formed in the trench 23 formedin the N⁻-type layer 22, thereby constituting a semiconductor substrate.This semiconductor substrate is structured so that the N⁻-type layer 22includes therein voids 25 in the alignment region of the N⁻-type layer22. These voids 25 are formed with an equal interval for example.

In the semiconductor substrate having the structure as described above,the voids 25 formed in the alignment region can be optically recognizedto the N⁻-type layer 22 made of single crystal silicon. Thus, the voids25 can be used as an alignment mark to form the trenches 23 in theN⁻-type layer 22 provided in the semiconductor substrate, for example.This can provide alignment for a semiconductor apparatus formanufacturing a MOSFET and a super junction MOSFET having athree-dimensional structure.

Next, the following section will describe a method for manufacturing asemiconductor apparatus using a semiconductor substrate including themethod for manufacturing the semiconductor substrate having thestructure as described above. FIG. 4 is a sectional view of manufacturesteps of a semiconductor apparatus using a semiconductor substratemanufactured by manufacture steps including the manufacture steps of thesemiconductor substrate shown in FIG. 3.

First, in a step shown in FIG. 4( a), the N⁺-type substrate 21 made ofsingle crystal silicon is prepared and the N⁻-type layer 22 isepitaxially grown on the N⁺-type substrate 21. Then, a mask material 30such as resist is arranged on the surface of the N⁻-type layer 22. Then,in the alignment region, a part of the mask material 30 at which thevoids 25 as an alignment mark are to be formed is opened. As a result,openings having an equal width are formed in the mask material 30 withan equal interval for example.

In a step shown in FIG. 4( b), the N⁻-type layer 22 covered by the maskmaterial 30 is etched to form trenches 31 having an equal width in thealignment region of the N⁻-type layer 22 with an equal interval forexample based on conditions in which the trenches 31 have a widthsmaller than that of the trenches 23 (e.g., smaller than 1 to 50 μm) orthe trenches 31 are deeper than the trenches 23 (e.g., 1 to 50 μm ormore). In the case of the second embodiment, the trenches 31 have awidth smaller than that of the trenches 23 and the trenches 31 areformed to a depth at which the N⁺-type substrate 21 can be etched sothat the trenches 31 are deeper than the trenches 23. The trenches 31may be etched by an anisotropic dry etching using RIE or an anisotropicwet etching using TMAH or KOH for example.

In a step shown in FIG. 4( c), the mask material 30 is removed tosubsequently form an oxidized film 32 by thermal oxidation or CVD or thelike as mask material on the surface of the N⁻-type layer 22. This stepalso may be performed so as to form the oxidized film 32 not only on thesurface of the N⁻-type layer 22 but also in the trenches 31. In thiscase, the oxidized film 32 may be formed in the entirety or a part ofthe interior of the trenches 31. Thereafter, in the device formationregion, a desired position of the oxidized film 32 is etched and openedby using the trenches 31 as an alignment mark to provide alignment withthe etching mask of the oxidized film 32. Thus, the desired position ofthe oxidized film 32 can be accurately opened. Then, the oxidized film32 used as mask material is etched to form the trenches 23 in theN⁻-type layer 22 with an equal interval.

In a step shown in FIG. 4( d), the oxidized film 32 is removed. At thistime, the oxidized film 32 arranged in the trenches 31 may be removedimperfectly. Then, a P⁻-type epitaxial film 33 for example is formed soas to bury the trenches 23 formed in the N⁻-type layer 22 based onconditions according to which a rate control can be provided to promotethe growth of the epitaxial film 33 into the trenches 23 formed in theN⁻-type layer 22. The conditions are the same as those of theabove-described step of FIG. 2( e) of the first embodiment.

As a result, the epitaxial film 33 is buried in the trenches 23 thathave a width larger or smaller than that of the trenches 31. Thus, thetrenches 31 are not perfectly buried by the epitaxial film 33, leavingthe voids 25.

Thereafter, in a step shown in FIG. 4( e), an uneven part of theepitaxial film 33 is eliminated by a planarization processing step byCMP for example. As a result, the epitaxial film 33 is left in thetrenches 23 to form the impurity diffused layer 24.

Then, as shown in a step of FIG. 4( f) for example, as in the step ofFIG. 2( g) of the first embodiment, a subsequent step of manufacturingthe remaining semiconductor apparatus is performed by forming theN⁻-type layer 26 on the N⁻-type layer 22 and the impurity diffused layer24 for example to complete the semiconductor apparatus using thetrenches 23 having a high aspect ratio. This step also uses the voids 25as an alignment mark to provide alignment with a subsequentphotolithography step. Thus, the respective components constituting thesemiconductor apparatus can be formed at desired positions accurately.

As described above, in the semiconductor substrate of the secondembodiment, the voids 25 formed in the N⁻-type layer 22 can be used asan alignment mark. Thus, the semiconductor substrate as described abovecan be used to provide alignment in the subsequent step of manufacturinga semiconductor apparatus. Thus, the respective components constitutingthe semiconductor apparatus can be formed at desired positionsaccurately.

Third Embodiment

The following section will describe the third embodiment of the presentinvention. The third embodiment simultaneously forms the trenches 31 forforming the voids 25 used as an alignment mark shown in the secondembodiment and the trenches 23 for forming the impurity diffused layer24 having a high aspect ratio. Thus, the following section will describea difference of the third embodiment from the second embodiment and thesame structures as those of the second embodiment will not be furtherdescribed.

FIG. 5 is a sectional view of manufacture steps of a semiconductorapparatus using a semiconductor substrate manufactured by manufacturesteps including the manufacture steps of a semiconductor substrateaccording to the third embodiment of the present invention.

First, in a step shown in FIG. 5( a), the same step as theabove-described step of FIG. 4( a) is performed to form the N⁻-typelayer 22 on the surface of the N^(f)-type substrate 21 to furtherarrange the mask material 30 on the surface of the N⁻-type layer 22.Then, in the alignment region, a part of the mask material 30 at whichthe voids 25 as an alignment mark are to be formed is opened and a partin the device formation region at which the trenches 23 are to be formedin the mask material 30 is opened.

Next, in a step shown in FIG. 5( b), the N⁻-type layer 22 covered by themask material 30 is etched to simultaneously perform the formation ofthe trenches 31 in the alignment region of the N⁻-type layer 22 and theformation of the trenches 23 in the device formation region of theN⁻-type layer 22 so that the trenches 31 have a width smaller than thatof the trenches 23 (e.g., smaller than 1 to 50 μm).

In a step shown in FIG. 5( c), the mask material 30 is removed tosubsequently form the P⁻-type epitaxial film 33 for example so as tobury the trenches 23 formed in the N⁻-type layer 22 based on conditionsaccording to which a rate control can be provided to promote the growthof the epitaxial film 33 into the trenches 23 formed in the N⁻-typelayer 22. The conditions are the same as those of the above-describedstep of FIG. 2( e) of the first embodiment.

As a result, the epitaxial film 33 is buried in the trenches 23 thathave a width larger than that of the trenches 31. Thus, the trenches 31are imperfectly buried by the epitaxial film 33 to leave the voids 25.

Thereafter, in a step shown in FIG. 5( d), the same step as that of FIG.4( e) is performed to form the impurity diffused layer 24.

Then, as shown in a step of FIG. 5( e) for example, the subsequent stepof manufacturing the remaining semiconductor apparatus is performed asin the step of FIG. 2( g) of the first embodiment by forming the N⁻-typelayer 26 on the N⁻-type layer 22 and the impurity diffused layer 24 forexample. As a result, the semiconductor apparatus using the trenches 23having a high aspect ratio is completed.

As described above, the third embodiment simultaneously performs theformation of the trenches 31 for forming the voids 25 as an alignmentmark and the formation of the trenches 23 for forming the impuritydiffused layer 24 having a high aspect ratio. This can eliminate a stepthat is required only to form the voids 25 as an alignment mark and thuscan simplify the manufacture steps of the semiconductor substrate andthe semiconductor apparatus.

Fourth Embodiment

The following section will describe the fourth embodiment of the presentinvention. The fourth embodiment forms the trenches 23 for forming theimpurity diffused layer 24 having a high aspect ratio to subsequentlyform the trenches 31 for forming the voids 25 used as an alignment markshown in the second embodiment. The following section will describe adifference of the fourth embodiment from the second embodiment. The samestructures as those of the second embodiment will not be furtherdescribed.

FIG. 6 is a sectional view of manufacture steps of a semiconductorapparatus using a semiconductor substrate manufactured by manufacturesteps including the manufacture steps of a semiconductor substrateaccording to the fourth embodiment.

In a step shown in FIG. 6( a), the same step as the above-described stepof FIG. 4( a) is performed to form the N⁻-type layer 22 on the surfaceof the N⁺-type substrate 21. Then, the same step as the step of FIG. 4(c) is performed to arrange the oxidized film 32 as mask material on thesurface of the N⁻-type layer 22. Thereafter, a part in the deviceformation region of the oxidized film 32 at which the trenches 23 are tobe formed is opened.

Next, in a step shown in FIG. 6( b), the N⁻-type layer 22 covered by theoxidized film 32 is etched to form the trenches 23 in the deviceformation region of the N⁻-type layer 22.

Next, in a step shown in FIG. 6( c), the oxidized film 32 is removed tosubsequently use the same step as the step of FIG. 4( a) to form themask material 30 on the surface of the N⁻-type layer 22. This step alsomay be performed so as to form the mask material 30 not only at thesurface of the N⁻-type layer 22 but also in the trenches 23. In thiscase, the mask material 30 may be formed in the entirety or a part ofthe interior of the trenches 31. Thereafter, a desired part in thealignment region of the mask material 30 is etched and opened. Then, theN⁻-type layer 22 covered by the mask material 30 is etched to form thetrenches 31 in the N⁻-type layer 22 with an equal interval.

Thereafter, in a step shown in FIG. 6( d), the same step as that of FIG.4( d) is performed to bury the epitaxial film 33 in the trenches 23 andto form the voids 25 as an alignment mark. In steps shown in FIG. 6( e)and FIG. 6( f), the same steps as those of FIG. 4( e) and FIG. 4( f) areperformed and the subsequent step of manufacturing the remainingsemiconductor apparatus is performed to complete the semiconductorapparatus using the trenches 23 having a high aspect ratio. These stepsalso use the voids 25 as an alignment mark to provide alignment in thesubsequent photolithography step. Thus, the respective componentsconstituting the semiconductor apparatus can be formed at desiredpositions accurately.

As described above, as in the fourth embodiment, the trenches 23 forforming the impurity diffused layer 24 having a high aspect ratio may beformed to subsequently form the trenches 31 for forming the voids 25used as an alignment mark.

Other Embodiments

The first embodiment has exemplarily described a semiconductor substratehaving the structure shown in FIG. 1 (specifically, the structure inwhich the N⁻-type layer 2 is formed on the surface of the N⁺-typesubstrate 1). However, another structure also may be used in which asemiconductor substrate for which steps up to the step of FIG. 2( f) arecompleted (i.e., a structure in which the impurity diffused layer 5 isformed in the trench 4). Similarly, the second embodiment also may use asemiconductor substrate having a structure in which the trenches 23 arenot yet formed (i.e., a structure for which steps up to the step of FIG.4( b) are completed).

The above respective embodiments have described a case where only theimpurity diffused layers 5 and 24 each of consisting of one layer areformed in the trenches 4 and 23 formed in the device formation region.However, the impurity diffused layers 5 and 24 also may be composed of aplurality of conductivity-type layers or layers having differentconcentrations.

Although the above respective embodiments have described a case wherethe N⁻-type layers 2 and 22 are formed on the N⁺-type substrates 1 and21, they are not limited to these conductivity types. For example, asemiconductor substrate and a semiconductor layer formed on thesemiconductor substrate also may be both the P-type ones or also may beof different conductivity types.

Fifth Embodiment

The following section will describe the fifth embodiment of the presentinvention.

As shown in FIG. 7, the semiconductor substrate includes an N⁺-typesubstrate body 63. Epitaxial films 61 and 66 are formed on the substratebody 63. The substrate body 63 is an N⁺-type silicon single crystalsubstrate doped with impurity such as phosphorus, arsenic, or antimony.The epitaxial films 61 and 66 are an N-type silicon single crystal layerdoped with impurity such as phosphorus, arsenic, or antimony. Theepitaxial films 61 and 66 are partially removed by etching to form therib-shape epitaxial films 61 and 66 on the surface of the substrate body63 with a predetermined interval. Trenches 64 and 67 among the epitaxialfilms 61 and 66 are filled with epitaxial films 62 and 68 consisting ofP-type silicon single crystal doped with impurity such as boron,gallium, or indium.

The following section will describe a method for manufacturing such asemiconductor apparatus of the present invention. First, as shown inFIG. 7( a), the 1\e-type substrate body 63 is prepared to form the firstN-type first epitaxial film 61 thereon. Specifically, the firstepitaxial film 61 is grown in a temperature range of 400 to 1200 degreeswhile supplying silane gas as raw material gas to the surface of thesubstrate body 63.

Next, as shown in FIG. 7( b), the first epitaxial film 61 is partiallyetched to form the first trenches 64. Specifically, a silicon oxidizedfilm (not shown) is formed on the first N-type epitaxial film 61 topattern this silicon oxidized film so as to have a predetermined trenchhaving a predetermined shape. This patterned silicon oxidized film isused as a mask to subject the first N-type epitaxial film 61 to ananisotropic etching (RIE) or a wet etching by alkaline anisotropicetching liquid (e.g., KOH, TMAH) to form the first trenches 64.Thereafter, the silicon oxidized film (not shown) used as a mask isremoved. In this manner, the first epitaxial films 61 having a rib-shapeare formed on the surface of the substrate body 63 with a predeterminedinterval and the first trenches 64 are formed among the first epitaxialfilms 61, respectively.

Next, as shown in FIG. 7( c), the second epitaxial film 62 is grown onthe surface of the first epitaxial film 61 except for the entireinterior of the first trenches 64 and the first trenches 64.Specifically, the vapor growth method is used to form the secondepitaxial film 62 in a temperature range of 400 to 1150 degrees whilesuppressing raw material gas to the first epitaxial film 61 includingthe inner face of the first trenches 64 and the second epitaxial film 62is buried in the first trenches 64. In the step of burying the secondepitaxial film 62 in the first trenches 64 (at least in the finalburying step), mixed gas of semiconductor source gas and halide gas ispreferably used as raw material gas supplied for the formation of thefirst epitaxial film 61. Semiconductor source gas may include monosilane(SiH₄), disilane (Si₂H₆), dichlorosilane (SiH₂Cl₂), trichlorosilane(SiHCl₃), or silicon tetrachloride (SiCl₄) for example. In particular,the semiconductor source gas is preferably any of dichlorosilane(SiH₂Cl₂), trichlorosilane (SiHCl₃), or silicon tetrachloride (SiCl₄).Halide gas is preferably any of hydrogen chloride (HCl), chlorine (Cl₂),fluorine (F₂), chlorine trifluoride (CIF₃), hydrogen fluoride (HF), andhydrogen bromide (HBr) and is more preferably hydrogen chloride (HCl) inparticular.

When mixed gas of semiconductor source gas and halide gas is supplied asraw material gas, halide gas thereof functions as etching gas. Theetching gas is provided with a controlled supply rate so that theetching rate is higher at the opening of the first trenches 64 than atthe interior of the first trenches 64. As a result, the growth rate islower at the opening of the first trenches 64 than at a deeper portion.Thus, with regards to the second epitaxial film 62 on the side faces ofthe first trenches 64, the bottom part of the first trenches 64 has alarger thickness than that of the opening of the first trenches 64.Thus, as shown in FIG. 2( c), the second epitaxial film 62 can be buriedin the first trenches 64 without causing a void in the first trenches64.

Next, as shown in FIG. 7( d), the second epitaxial film 62 is polishedto expose the surface of the first epitaxial film 61 and to planarizethe upper face of the second epitaxial film 62 buried in the entireinterior of the first trenches 64. This polishing can be performed byCMP for example.

Next, as shown in FIG. 7( e), the third epitaxial film 66 having thesame composition as that of the first epitaxial film 61 is further grownon the planarized upper face of the second epitaxial film 62 and theexposed face of the first epitaxial film 61. This formation of the thirdepitaxial film 66 is performed by the same procedure as that of theformation of the first epitaxial film 61. Specifically, the vapor growthmethod is used to grow the third epitaxial film 66 in a temperaturerange of 400 to 1200 degrees while supplying silane gas as raw materialgas to the planarized upper face of the second epitaxial film 62 and theexposed face of the first epitaxial film 61.

Next, as shown in FIG. 7( f), parts of the third epitaxial film 66corresponding to the first trenches 64 are etched to form the secondtrenches 67 to extend the first trenches 64. Specifically, a siliconoxidized film (not shown) is formed on the third epitaxial film 66 and apart of this silicon oxidized film corresponding to the first trench 64is removed and is patterned to have a predetermined shape. Then, thispatterned silicon oxidized film is used as a mask to subject the thirdepitaxial film 66 to an anisotropic etching (RIE) or a wet etching byalkaline anisotropic etching liquid (e.g., KOE, TMAH) to form the secondtrenches 67 to extend the first trenches 64. Thereafter, the siliconoxidized film (not shown) used as a mask is removed.

Next, as shown in FIG. 7( g), the fourth epitaxial film 68 is furthergrown on the entire interior of the second trenches 67 and the surfaceof the third epitaxial film 66 other than the second trenches 67. Thisformation of the fourth epitaxial film 68 is performed by the sameprocedure as that of the above-described formation of the secondepitaxial film 62. Specifically, the vapor growth method is used to formthe fourth epitaxial film 68 in a temperature range of 400 to 1150degrees while supplying raw material gas to the third epitaxial film 66including the inner face of the second trenches 67 to bury the fourthepitaxial film 68 in the second trenches 67.

Next, as shown in FIG. 7( h), the fourth epitaxial film 68 is polishedto expose the surface of the third epitaxial film 66 and the upper faceof the fourth epitaxial film 68 buried in the entire interior of thesecond trenches 67 is planarized. As a result, a semiconductor substrateis obtained in which a P-type region and an N-type region arealternately arranged in the lateral direction.

Whether the epitaxial films 62 and 68 can be buried in the trenches 64and 67 without causing a void or not depends on an aspect ratio (B/A)that is represented by a depth B of the trenches 64 and 67 to a width Aof the trenches 64 and 67. The shallower depth B the trenches 64 and 67have to the width A of the trenches 64 and 67 (i.e., the smaller aspectratio (B/A) is), the epitaxial films 62 and 68 can be more securelyburied in the trenches 64 and 67 without causing a void. According tothe method for manufacturing a semiconductor substrate of the presentinvention, the formation of the trenches 64 and 67 and the burying ofthe epitaxial films 62 and 68 are performed in a plurality of steps.Thus, the aspect ratio of the trenches 64 and 67 when the epitaxialfilms 62 and 68 are buried can be reduced. As a result, the epitaxialfilms 62 and 68 can be buried in the trenches 64 and 67 without causinga void.

In the fifth embodiment, it was described that the formation of thetrenches 64 and 67 and the burying of the epitaxial films 62 and 68 areperformed in two steps. When an aspect ratio of trenches finally to beobtained is relatively high, however, the above-described step (g) alsomay be followed by the repetition of the step (d) to step (g) one or twotimes. A method for manufacturing a semiconductor substrate forrepeating the step (d) to the step (g) three times or more can reduce,even when an aspect ratio of trenches finally to be obtained isrelatively high, an aspect ratio of the tranches for burying theepitaxial film in one time can be reduced. This can effectively preventa void from being generated in the epitaxial film buried in thetrenches.

INDUSTRIAL APPLICABILITY

The present invention can be used for a semiconductor substrate that isused for a semiconductor apparatus using a trench formed with a highaspect ratio in the depth direction of the substrate (e.g., a MOSFET anda super junction MOSFET having a three-dimensional structure) and themethod for manufacturing thereof.

The invention claimed is:
 1. A method for manufacturing a semiconductorsubstrate, comprising: preparing a substrate made of a single crystalsemiconductor; forming a semiconductor layer made of a single crystal onthe surface of the substrate; arranging, on the semiconductor layer, afirst mask material having an opening formed in an alignment region inthe semiconductor layer different from a device formation region;etching the semiconductor layer, covered by the first mask material, toform an alignment mark formation trench in the alignment region;removing the first mask material to subsequently arrange, on a surfaceof the semiconductor layer, a second mask material having an openingformed in the device formation region of the semiconductor layer;etching the semiconductor layer, covered by the second mask material, toform a device trench in the device formation region; removing the secondmask material to subsequently bury an epitaxial film in the devicetrench to form voids in the alignment mark formation trench; andsubjecting a part of the epitaxial film that is formed outside of thedevice trench to a planarization processing.
 2. The method formanufacturing a semiconductor substrate according to claim 1, whereinthe alignment mark formation trench has a depth deeper than a width ofthe device trench.
 3. The method for manufacturing a semiconductorsubstrate according to claim 2, wherein the alignment mark formationtrench is formed to have a depth at which the substrate can be etched.4. The method for manufacturing a semiconductor substrate according toclaim 3, wherein the alignment mark formation trench has a width smallerthan the device trench.
 5. The method for manufacturing a semiconductorsubstrate according to claim 2, wherein the alignment mark formationtrench has a width smaller than the device trench.
 6. The method formanufacturing a semiconductor substrate according to claim 1, whereinthe alignment mark formation trench has a width smaller than the devicetrench.
 7. A method for manufacturing a semiconductor substrate,comprising: preparing a substrate made of a single crystalsemiconductor; forming a semiconductor layer made of single crystal onthe surface of the substrate; arranging a first mask material on thesurface of the semiconductor layer, the first mask material including anopening formed in a device formation region of the semiconductor layer;etching the semiconductor layer, covered by the first mask material, toform a device trench in the device formation region; removing the firstmask material to subsequently arrange, on the semiconductor layer, asecond mask material including an opening in an alignment region in asemiconductor layer different from a device formation region; etchingthe semiconductor layer, covered by the second mask material, to form analignment mark formation trench in the alignment region; removing thesecond mask material to subsequently bury an epitaxial film in thedevice trench to form voids in the alignment mark formation trench; andsubjecting a part of the epitaxial film that is formed outside of thedevice trench to a planarization processing.
 8. The method formanufacturing a semiconductor substrate according to claim 7, whereinthe alignment mark formation trench has a depth deeper than a width ofthe device trench.
 9. The method for manufacturing a semiconductorsubstrate according to claim 7, wherein the alignment mark formationtrench has a width smaller than the device trench.